This invention relates to ultrasonic diagnostic imaging systems and, in particular, to ultrasonic diagnostic imaging systems which produce spatially compounded images of Doppler signal information.
My U.S. Pat. No. 6,210,328 describes apparatus and methods for performing real time spatial compounding of ultrasonic diagnostic images. Spatial compounding is an imaging technique in which a number of ultrasound images of a given target that have been obtained from multiple vantage points or angles are combined into a single compounded image by combining the data (e.g., by linearly or nonlinearly averaging or filtering) at each point in the compound image which has been received from each angle. The compounded image typically shows lower speckle and better specular reflector delineation than conventional ultrasound images from a single viewpoint.
In a constructed implementation an ultrasonic transducer scans a target from a number of different perspectives. For example, several sector images can be sequentially acquired by a phased array transducer, each with an apex located at a different point along the array. As a second example a steered linear array can be used to image the target with a sequence of groups of beams, each group steered at a different angle with respect to the axis of the array. In either case the received images are processed in the usual way by beamforming and detection and stored in a memory. To form the compound image the images are spatially aligned (if not already aligned by a common beam steering reference, for instance) by spatially correlating the image data. The common spatial locations in the images are then compounded by averaging or summing and the resultant compound image is displayed.
The improvements in image quality afforded by spatial compounding are a function of the number of echoes from different look directions which are compounded at the various points in the image field. As my aforementioned patent application describes, a scanhead array of finite size will produce an image region in which maximal spatial compounding occurs, referred to therein as the region of maximum image quality (RMIQ). The RMIQ is in turn a function of the number of look directions and the angular range traversed by the different look directions. It is desirable to have a RMIQ which is as large as possible with the RMIQ covering a substantial portion of the image field.
In accordance with the principles of the present invention, spatial compounding is performed by use of a curved array scanhead. In one embodiment the beams of the different look directions are steered in parallel groups, affording an ease in image scan conversion. In another embodiment the beams of the different look directions are radially steered by taking advantage of the array curvature, affording an ease in beamforming and image scan conversion, improved sampling uniformity, an improvement in the RMIQ size, and improved signal to noise ratio.